Surfactant systems incorporating rod-like or wormlike micelles are widely utilized in both industrial and consumer products. While the viscoelastic behavior of such systems provides desired aesthetic and end-use properties, there is often a need to further modify the rheological properties of such systems for certain applications. These wormlike micelle (WLM) systems behave much like polymer systems. Furthermore, incorporation of nano-sized particles can interact with the large polymer-like WLM structures to alter rheological behavior. While there are number of studies that have focused on the effect of particles on rheological behavior in cationic surfactant systems, fewer studies have been done on systems containing anionic surfactants. In this study, relaxation behaviors in systems containing sodium alkyl ether sulfate and sodium carbonate were studied. The anionic surfactant was commercial grade material with an average chain length of twelve carbons and one ethoxy (EO) group. WLM behavior was achieved through the addition of sodium carbonate. Ludox® TMA, a nano-sized colloidal silica, was employed at different concentrations in the WLM systems. Temperature was varied between 5 and 45<sup>o</sup>C. Relation was characterized in terms of the Maxwell model, but was was only found to adequately describe data below the threshold of ωτ ~ 1.  The Maxwell model failed to describe behavior at higher frequencies. A modified expression with an additional relaxation mode adequately described relaxation throughout the frequency range studied. It was also found that zero-shear viscosities generally increased with an increase in silica concentration, and relaxation times decreased. The decrease in relaxation time is in contrast to results from some studies, but is in agreement with others. Preliminary results of measurements of relaxation due to a compressive stress via ultrasonic attenuation measurements in the surfactant/particle systems are also discussed.

Viscoelastic behavior of alkyl ether sulfate systems containing nano-sized colloidal silica

253rd National Meeting (2017)

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